Benjamin Eberlei has a new post to his site today answering a question he sometimes gets about using Doctrine2 in a SOLID context (more on SOLID development here) as it seems difficult to follow the Single Responsibility Principle with how the tool is used.

These problems are related to the inability to share behavioral code through aggregation and the complexity of state transformations. Combining both, your average entity with 5-15 fields can end up with hundrets or thousands lines of code. The solutions to both problems boil down to minimizing duplication and maximizing clarity.

He looks at two different kinds of objects Doctrine uses in its setup, the value objects and method objects, and "maximize clarity" on them by dividing them up into more functional-related objects, passed into each other via method injection.